DEMONSTRATION OF AXIAL GRADIENTS. 139 



algae. Some sort of physiological correlation undoubtedly 

 exists, and whatever its nature, it apparently gives rise to the 

 same sort of order and unity as in other axiate forms. It can 

 scarcely be supposed that in this case the correlation is accom- 

 plished by chemical substances given off by the individual 

 diatoms, and the only other possibility is a transmissive relation 

 of some sort, probably electrical in character (see R. S. Lillie, 



'17). 



Among the protozoa observations have been made on Noctiluca, 



Paramecium, Stentor and Spirostomum. In Noctiluca the first 

 traces of color appear on the surface of the membrane in the 

 mouth region and the color spreads gradually over the membrane. 

 The entoplasm later contracts and disintegrates into droplets 

 before staining, but some slight indications of a basipetal gradient 

 appear in this disintegration. The thickened flagellum of 

 Noctiluca shows a well marked basipetal gradient. 



In Stentor the color gradient in the ectoplasm is essentially 

 the same as the susceptibility gradient already described (Child, 

 '14), i. e., basipetal, but the permanganate indicates a slight 

 degree of " dorso-ventral " difference in that the staining pro- 

 gresses basipetally more rapidly on the oral than on the opposite 

 side of the body. This difference along different meridians of 

 the body has not been observed in susceptibility agents. 



Spirostomum shows an ectoplasmic basipetal gradient both in 

 color and in disintegration in permanganate, a short gradient in 

 the opposite direction appearing at the basal end in a varying 

 percentage of individuals. Other agents give essentially similar 

 results. The secondary gradient in this form is very probably 

 associated with the reversibility in the direction of locomotion 

 which this species shows to a very high degree and with stimula- 

 tion or irritation by the reagent for it apparently occurs only in 

 those individuals which contract strongly and repeatedly in the 

 solution. 



In Paramecium the first effect of permanganate is, even in 

 very low concentrations, a contraction of the ectoplasm beginning, 

 and most extensive at the anterior end. This results in approach 

 to spherical form, and in the lower concentrations the body often 

 bursts either in the "anal" region or near one of the vacuoles. 



